1. Field of the Invention
This invention relates to gas-cooled field windings of synchronous dynamoelecric machines, and more particularly, to means for cooling those gas-cooled windings by use of dual axial flow blowers, each of which actively function for one rotational direction of the dynamoelectric machines.
2. Description of the Prior Art
Large inner-cooled hydrogenerators often use a gas coolant for the field winding in end ventilated machines and rim ventilated machines. End ventilated machines are provided with radial vents in the stator so that coolant gas enters both ends of the rotor, passes between the rotor poles into the air gap between the rotor and the stator, and then through radially disposed stator vents. End ventilated machines have a centrifugal blower attached to the rotor on each axial end while the rim ventilated machines function by having radial openings formed in the rotor which cause the rotor to act as a radial flow centrifugal blower forcing the air through the rim openings and into the interpolar space where it contacts the field winding.
Disadvantages of the rim ventilated machines include coolant pressure limitations inherent in single stage radial-flow blowers and a smaller effective stress area for the rotor rim due to the formation of radial vent openings. End ventilated machines usually have single stage centrifugal blowers due to the fact that staging centrifugal blowers requires complex machining, is expensive, and impractical due to axial space limitations imposed on many dynamoelectric machines such as pump-storage hydrogenerators. Thus, centrifugal blowers on end ventilated designs encounter a coolant pressure limitation as did the rim ventilated design.
The low pressure developed by end ventilated and rim ventilated designs limit the coolant flow velocity passing the field winding resulting in a motor-generator whose power rating is constrained by the high temperature existing in the field winding. Desirable features on rotatively reversible dynamoelectric machines such as hydrogenerators include increased coolant pressure and velocity to allow significant up-rating for dynamoelectric machines of any given size while retaining their capability of cooling the field winding for each rotational direction. A further desirable characteristic would be to decrease the stresses now experienced by the rotor rim on machines utilizing rim ventilation.